The effect of gangliosides on the lamellar phase behaviour of phosphatidylethanolamines.

The thermotropic properties of aqueous phosphatidylethanolamine dispersions vary with hydration. Measured by EPR-spectroscopy freshly hydrated dimyristoylphosphatidylethanolamine dispersions exhibit a gel to liquid-crystalline phase transition at Tml = 48 degrees C. Dehydration could be induced by prolonged incubation of a hydrated sample at 4 degrees C. The phase transition temperature of the dehydrated phase was determined to be Tmh = 54 degrees C. From the measured phase transition curves we followed the dehydration with time and found a cooperative nucleation process. A 50% dehydration was reached after 5 days. This dehydration process could be prevented by gangliosides: 1.5 mol% of GT1b, 4 mol% of GM1 or 7 mol% of GD1a or GM3 but also 7 mol% of phosphatidic acid were able to stabilize the hydrated phase completely. The effect of gangliosides GM1, GM3, GD1a, GT1b and of the negatively charged phosphatidic acid on the phase behaviour of dimyristoylphosphatidylethanolamine (DMPE) dispersions were investigated. The phase transition temperature of freshly hydrated DMPE samples was successively decreased from 48 to 43 degrees C with increasing amounts of GD1a up to 10 mol% whereby the phase transition was significantly broadened. Gangliosides GM1, GM3 and GT1b as well as phosphatidic acid had minor effects. Dispersions of pure DMPE prepared below the transition temperature Tml form the dehydrated phase again with a melting temperature of Tmh = 54 degrees C. In the presence of 10 mol% GD1a or GT1b this value is reduced to Tml, the phase transition temperature of the hydrated phase. The reduction induced by GM3 is less pronounced. With GM1 or phosphatidic acid the samples remain partially dehydrated and the phase transition curves become biphasic up to 7 mol% ganglioside or phosphatidic acid.